Picture the Murrah federal building after Timothy McVeigh blasted it to kingdom come with a fertilizer bomb. Now imagine bombs that powerful, or even stronger, deployed against the Canadian parliament and other Ontario landmarks. According to Canadian police, that's what Islamist terrorists arrested over the weekend planned to do with fertilizer — three times the amount McVeigh used — they were allegedly trying to procure.

The bombshell that did go off was the revelation that most of the 17 Muslim suspects arrested in the plot, including five juveniles, were Canadian citizens, apparently acting on their own initiative. According to a classified Canadian Security Intelligence Service report leaked early last week, law enforcement authorities say the next phase in the terror war involves an increasing number of "home-grown" Islamic radicals.

"The implications of this shift are important," said the report, in what is surely an understatement. It's one thing to work to deport foreign-born radicals, or to keep them from entering Britain, Canada or the United States (where the recent arrest of two American Muslims in Georgia has been tied to the alleged Canadian plot). It is quite another when those planning terror attacks hold citizenship here and fit in socially in ways that foreigners do not.

Even more frightening is the warning in the Canadian security report that terror organizers are actively seeking out Western converts to Islam "for their familiarity with the West and relative ease at moving through Western society." This means that none of us — Muslim and non-Muslim — can afford to turn a blind eye to radical Islamist speech. One of the Canadian terror suspects is reportedly a fire-breathing Islamist whose lectures at a Toronto mosque radicalized middle-class young Canadians in his circle — some of whom now face charges along with their mentor. According to the Toronto Star, the Wahhabist rhetoric of the oldest suspect, Qayyum Abdul Jamal, 43, alarmed members of the center's board, but they tolerated it.

Among Muslims and broader society both, benign tolerance of radicalism has got to stop — before many more innocent lives are lost.